The invention relates to an x-ray diagnostic generator having a regulator circuit for the x-ray tube voltage which contains a comparator element for comparing the actual value of the x-ray tube voltage with a set point value, and also a control element responsive to the output signal of the comparator element for controlling the heating current of the x-ray tube in order to adjust the actual value of the x-ray tube voltage to the set point value.
An x-ray diagnostic generator of this type is described in the U.S. Pat. No. 3,974,387. In such an x-ray diagnostic generator, the voltage drop in the generator internal impedance is adjusted such that the respectively desired x-ray tube voltage is connected to the x-ray tube. If, for example, the actual value of the x-ray tube voltage in comparison to the set point value is too high, an increase of the x-ray tube current results. The voltage drop in the internal impedance of the x-ray generator increases thereby and the x-ray tube voltage decreases. In reverse, an increase of the x-ray tube voltage results by the reduction of the x-ray tube current.
It is known that an optimum utilization of the loadability of the x-ray tube, and thus a very short exposure time for the x-ray pictures can be obtained when an x-ray diagnostic generator is operated with a decreasing (falling) load characteristic wherein the x-ray tube output is exponentially decreased to a constant value from a peak value at the beginning of an x-ray exposure. Thereto, for example, it is known from the German Offenlegungsschrift 2,122,138, to exponentially decrease the x-ray tube current from a peak value at the beginning of an x-ray picture according to the course of the highest permissible x-ray tube power output. However, this principle cannot be utilized in an x-ray diagnostic generator of the initially mentioned type, as the x-ray tube current is indeed called upon to regulate the x-ray tube voltage.